Pour the cream into the blender container and cover. Blend on the lowest speed until the cream begins to thicken around the blades. While continuing to blend, pour the ice water through the opening in the lid. Raise the speed to the 4th lowest speed and blend until butter forms, about 2 minutes longer. Transfer the butter into a strainer to drain.Salt to taste Then pack it into a butter mold or form into squares and chill.